As long as mankind has utilized sharpened devices and cutting instruments such as knives and blades there has been a need for methods and devices for keeping those devices sharp.
Many sharpening devices have been proposed over the years, utilizing a wide variety of sharpening blade shapes and sharpening angles. Some sharpeners utilize round sharpening blades, such as U.S. Pat. No. 4,112,790 to Marder, and U.S. Pat. No. 5,377,563 to Weeks. Due to the radial nature of the sharpening blades these devices do not provide a true "V" shaped edge to the sharpened device, and therefore do not achieve the best shape or durability for the sharpened workpiece.
Other devices rely upon abrasive-type sharpening elements, such as U.S. Pat. No. 4,530,188 to Graves. However, due to the inherently inexact nature of the shape of the sharpening elements, and in particular as extended use wear causes the shape to change, these type of devices also are unable to ensure that the optimal "V" shaped edge results.
Sharpeners have been proposed that utilize beveled metallic sharpening elements, in a variety of shapes. For triangular elements, see U.S. Pat. No. 4,599,919 to Fortenberry, and U.S. Pat. No. 562,223 to Hausse. For square elements, see U.S. Pat. No. 584,933 to Friedrich. While previously proposed devices of this type can obtain the desired "V" shaped edge, they do not precisely position the sharpening elements to provide the best degree of angle to the sharpened edge. And while some allow the sharpening elements to be rotated or exchanged to provide fresh sharpening edges, they do not increase the sharpener element utilization. They also do not increase the useful life of the sharpening elements.